The interaction of an anticancer agent with its primary target represents only the first step in the drug's mechanism of action. Knowledge of the apoptotic signaling mechanisms subsequently induced is of critical importance if advances are to be made in improving the effectiveness of these agents. The overall goal of our research is to improve cancer chemotherapy by understanding the nature and regulation of these apoptotic signaling pathways. Specifically, we are interested in defining the role of the stress-activated, c-Jun NH2-terminal protein kinase (JNK) in the mechanism of action of antimitotic anticancer drugs, particularly vinblastine. In Specific Aim 1 we will specifically inhibit JNK signaling to c-Jun/AP-1 and examine the effects of AP-1 inhibition on vinblastine-induced apoptosis and on gene expression in order to identify putative AP-1 target genes. Specific Aim 2 will test the relevant AP-1 target genes as intermediates in vinblastine-induced apoptosis, using a combination of molecular and cellular approaches. Completion of this aim will provide experimental verification of the role of the candidate genes identified, and a better understanding of the mechanisms of apoptotic signaling by vinblastine-activated JNK/AP-1. Specific Aim 3 will utilize chromatin immunoprecipitation to demonstrate recruitment of c-Jun to the regulatory regions of the relevant AP-1 target genes, and to identify novel regulatory partners that may cooperate with c-Jun. Specific Aim 4 will utilizec-jun-/- immortalized fibroblasts as a unique model system to further explore the role of c-Jun in the cellular response to vinblastine. This research will provide molecular insight into the role of JNKJc-Jun in vinblastine-induced apoptosis, and contribute to our basic understanding of the mechanism of action of this and related agents. In turn, this research may suggest novel approaches to alter the threshold for cell death to make these drugs more effective, lessening toxicity and improving specificity.